Avoiding Vne

Edward Downham wrote:

It is important to note that this margin is there to cope with things such as
ASI position and calibration errors. When you fly a glider at an _indicated_
speed of Vne, you might actually be nearer Vd and the realm of the test pilot.

No. VNE is an indicated airspeed limit (IAS). If there is a airspeed
calibration error, VNE has been reduced to correct it. The margin is
there for instrumental errors, and *pilot* errors.


As Bill Dean has mentioned, some gliders lose a lot of their control authority
over Vd. You may find yourself flying faster and faster and unable to do much
about it. Also, the faster you get, the more likely you are to overstress the
airframe with control inputs (and I don't just mean the elevator).

Have you any reference for this affirmation ? THis is a know issue on
earlier delta wings, also in earlier near-transsonic aircraft, but I
don't know any glider with such a problem.

In most modern gliders you should be able to pull 6g+ without breaking any bits
off them.

Not at VNE !!!

The rise is drag is high, and will pretty certainly arrest any
further speed build-up and bring the nose up quite smartly. Also you won't get
so close to the ground, if this is a factor.

The drag rise is not enough to avoid overspeeds. The rise in drag
provided by *airbrakes* (not pulling too hard) is the *only* way to
avoid either flutter (above VNE) or breaking the wings (by overloading).

Except when too close to the ground this is always the only thing to do.

And to come back to the original question, I think there is nothing to
fear pulling the airbrakes before getting out of the spin, since it will
help stopping the rotation (the outer airbrake will have a greater drag
due to greater airspeed)

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

On Sun, 28 Mar 2004 20:30:57 +0200, Denis
wrote:

Edward Downham wrote:

It is important to note that this margin is there to cope with things such as
ASI position and calibration errors. When you fly a glider at an _indicated_
speed of Vne, you might actually be nearer Vd and the realm of the test pilot.

No. VNE is an indicated airspeed limit (IAS). If there is a airspeed
calibration error, VNE has been reduced to correct it. The margin is
there for instrumental errors, and *pilot* errors.

Well, this one is just a little scary. For more than one glider of my
acquaintance Vne is given as a TAS in the manual. This can be
converted to IAS of course, but the IAS would, of course, decrease
with altitude.

Vstall, on the other hand, seems just about always to be given as an
IAS, and as an IAS the stall speed will remain about the same as
altitude increases. This is all pretty basic stuff I know, so I
probably misinterpreted your statement about Vne.

One way to look at the "coffin corner" situation where some very
high-flying aircraft, such as the U-2, I suppose, can end up at an
altitude where the stall speed, in TAS, has come very close to the
Vne, as a TAS.

Jim wrote in message

One way to look at the "coffin corner" situation where some very
high-flying aircraft, such as the U-2, I suppose, can end up at an
altitude where the stall speed, in TAS, has come very close to the
Vne, as a TAS.

More precisely, I think it's when the stall speed (IAS in the cockpit)
but really a TAS issue) approaches the limiting Mach number. Since
Mach vs TAS decreases with altitude, and TAS vs IAS increases with
altitude, the problem is inevitable for the right (or wrong, depending
on your point of view!) kind of plane.

Kirk

Jim wrote:

No. VNE is an indicated airspeed limit (IAS). If there is a airspeed
calibration error, VNE has been reduced to correct it. The margin is
there for instrumental errors, and *pilot* errors.


Well, this one is just a little scary. For more than one glider of my
acquaintance Vne is given as a TAS in the manual. This can be
converted to IAS of course, but the IAS would, of course, decrease
with altitude.

I did not want to raise the question of VNE at altitude (a more
difficult subject ;-) and the relation between IAS and TAS.

I replied to someone who mentioned the errors of static ports : The
calibrated airspeed (CAS) may be higher than the indicated airspeed
(IAS) depending og static ports location ; in that case, it is measured
during the tests and all limits are corrected to be given in *indicated*
airspeed.

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?